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BOGOTÁ – Half a mile above this city of almost eight million is a rugged, fog-shrouded world, silent except for the trickle of water and whispering wind pushing through the treeless tundra.

This is Chingaza, a national park 40 miles from Bogotá in the eastern range of the Colombian Andes.

Known as páramos, these ecosystems at more than 11,000 feet above sea level exist only in Central and South America, the majority in Colombia. Páramos resemble a sort of alpine archipelago, each a link in the chain of distinct island ecosystems that have evolved in isolation to produce plants found nowhere else on the planet. They play a crucial role in maintaining a reliable water supply for millions of people in major cities like Bogotá and Medellín. And along with the forests below, they protect those cities and the surrounding countryside from massive flooding.

One of the wettest countries on earth, Colombia has two rainy seasons. The second of the year officially began in September. For the past two years, however, some parts of the country have had little respite from a destructive deluge during what are traditionally drier times of year.

The Culprit

La Niña – the weather pattern that causes unusually cold ocean surface temperatures in the eastern Pacific – has been blamed as the immediate culprit. But scientists believe climate change is also a factor in the flooding that has affected three quarters of Colombia in the past two years, cost billions of dollars and left hundreds dead.

As climate change converges with human encroachment in these mountains, the degradation of high Andean ecosystems is accelerating. And there are growing concerns that these costly floods will become a chronic problem even if climate change leads to sustained drought in the region.

Páramos and cloud forests work as a finely tuned piece of ecological engineering that manages the flow of water from the high mountains to the lakes and rivers below. The páramos act as a sponge, absorbing and then conducting enormous quantities down the mountainside to the cloud forests. From there the water is further filtered and directed into rivers and reservoirs that quench the thirst of major urban areas without eroding the soil – crucial in protecting against flooding.

The annual precipitation in Chingaza, which provides about 80 percent of Bogotá's water, approaches four meters, or more than 13 feet, in some areas. Not all páramos are as wet as Chingaza, but they all have a vital role in both storing water and managing its flow.

Protecting Lowlands

"Well-preserved high-altitude lakes and peatlands help to protect lowlands from flooding by slowing down streamflows. After water purification, one of the most important regulating services of páramo...environments is flood control," said Daniel Ruiz, an associate professor of environmental engineering at Antioquia School of Engineering and researcher at Columbia University's International Research Institute for Climate and Society.

One of the most prominent features of páramos are large, silvery-green plants called espletia, more commonly known as frailejón. The plant is ubiquitous, dotting the chilly landscape in some places as far as the eye can see. Its spiky clusters of leaves, reminiscent of some cacti, are covered in soft little hairs that catch moisture from the fog and funnel it into moss-covered soils that can hold several times their weight in water.

There are a variety of theories about how rising air temperature and altered precipitation patterns might affect these ecosystems in the future. But change has already arrived.

In 2011, the Inter-American Institute for Global Change Research and the Scientific Committee on Problems of the Environment released a joint report assessing climate change and biodiversity in the Andes. The report notes that the region is not just facing threats from future climate change, but already undergoing "significant shifts in temperatures, rainfall regimes and seasonal weather patterns."

The extreme, prolonged rainy seasons in 2010 and 2011 offer a preview of the damage such shifts may bring to urban areas in the future. In Medellín, heavy rains created rivers in the city center and led to devastating landslides. In one case, more than 100 people were killed or missing after an avalanche of mud buried dozens of homes on a hillside above the city.

More Flooding

The Bogotá River, choked with sediment and trash, overflowed its banks and flooded low-lying neighborhoods in and around the nation's capital. All told, more than three million Colombians – about seven percent of the total population – were displaced or suffered significant damage to their homes in 2011 alone as a result of flooding, according the World Bank.

Models predict that warming in the Andes is likely to contribute both to more flooding and more drought in the region as mountain environments change. According to the Inter-American Institute report, the average temperature of the Andes has increased by 0.7 degrees Celsius over the past 60 years. That's similar to the global average, but high altitude ecosystems like páramos and cloud forests in the tropical Andes are particularly sensitive to warming – much like coral reefs, glaciers and polar regions.

Ruiz, who contributed to the report, noted that an analysis of weather records at one páramo research station showed increases in minimum temperatures were almost twice that of lower elevations, while increases in maximum temperatures jumped to nearly three times the average at lower elevations.

Climate change research here is in its early stages, and scientists are still teasing out which changes in the high mountains are the result of climate change and which are more likely the result of other human-caused changes, namely, agriculture, ranching and mining. Research suggests a combination of both is to blame for increasing temperatures and declines in key species, including some frailejónes.

Conrado Tobón, a hydrologist at the National University of Colombia in Medellín, studies how climate change is altering the water cycle of high Andean ecosystems. In 2005, his team began studying the eco-hydrology of páramos and high Andean forests that are crucial to the water supply of Bogotá, Medellín and Quito, Ecuador.

Confirming Results

The team took minute-by-minute measurements of conditions like precipitation, temperature, wind, evaporation rate and water content of the soil. The goal is to do a complete accounting of the movement of water from the time it hit the surface of a plant and passed through moss and soil, until it flowed out of the basin and into the network of high forest streams on its way to the lowlands.

They also used data on precipitation in Colombia from the Intergovernmental Panel on Climate Change (IPCC) to model changes under different temperature and precipitation scenarios. The researchers modeled for páramos degraded by agriculture and mining as well as protected ones like Chingaza. Tobón's results confirm what other models are showing: Precipitation will likely decrease in the páramos and high Andean forests, perhaps even leading to a sustained drought.

But overall drier conditions don't necessarily mean less risk of flooding – quite the opposite, in fact. At his own research stations in the northern Andes, Ruiz noticed increasing incidences of extreme rains, which are likely to cause more runoff and soil erosion. It's a perfect recipe for flooding.

"Dry periods are getting longer and wet seasons are getting more intense," he said. "Páramos are thus getting washed by intense, short-lived thunderstorms and downpours that cannot be handled by vegetation adapted to drizzles."

Lifting the Cloud Veil

Local climate changes are partly to blame. The conversion of mountain forest to pasture and croplands has raised temperatures in the region, prompting a lifting of the cloud level – enough to leave some cloud forests and páramos below the fog, and increasing solar radiation. This decrease in cloud cover is one of the biggest contributors to climatic stress in the páramos, according to Ruiz.

The convergence of local and global changes compounds the impacts on fragile but important high mountain ecosystems. Increased radiation and warmer temperatures cause plants normally found at lower elevations to move upslope. Invasive plant, animal and insect species also migrate, disrupting the delicate biological machinery that makes páramos and high forests function as a fine-tuned water storage and distribution system.

Instead of precipitation in the form of fog, páramos and forests receive more precipitation as rain. This affects the plants adapted to collecting moisture from fog and the soil, because they are unaccustomed to heavier rain droplets. Those heavier raindrops also compact the soil, causing it to absorb less water and increasing runoff and sediment, which clog rivers and contribute significantly to lowland flooding.

Awareness Grows

As awareness of climate change and other kinds of environmental degradation grows, the Colombian government is starting to respond. One example is a collaboration between the national government, the city of Bogotá and the environmental organization Conservation International on a páramo restoration project.

The plan calls for limiting local environmental degradation in protected areas, like Chingaza, through the creation of a 1.5 million-acre conservation corridor connecting the park with the nearby páramos of Guerrero and Sumapaz, the largest páramo in the world. It also seeks better protection of privately-owned lands in the vicinity that are being cleared for cattle ranching and potato farming.

Part of that scheme includes training for local farmers and ranchers in using more sustainable practices. Conservation International is developing a forest carbon project, using the sale of carbon credits to compensate landowners for setting aside portions of their land for conservation and forest restoration.

"We understand that these ecosystems are offering important services – not only the supply of water, but the regulation of water," said Patricia Bejarano-Mora, land-use planning coordinator for Conservation International's Colombia office.

"At this point maybe the solution is not works of engineering, like building dykes, but conservation of forests and eco-hydrology," she added. "Policies are beginning to recognize that."

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